I think the old ferts have a lot to do with it, but I'm not sure how much. Just give the one feeding of fish goo- too much, and it will inhibit flower, but you can't avoid it now that they are so far into N deficiency.
Use the ferts you've got now; this is definitely going to be chalked up to a learning experience. Next time you go to the hydro store, go with a shopping list, lol... Basic grow fert, basic bloom fert, bottle of GH Micro for emergencies, and if they carry a humic acid supplement, or another chelator like Clearex, that can be added to your flush solution, that helps release salts from the soil. FoxFarms is organic derived but still kinda chemmy. I find that the botanicare power plant/power flower line whichis very similar tends to be more stable. I'm currently growing with a set that expired like 4 years ago, hahaha!
Re-potting is going to help you. DEfinitely.